Nov. 19 (Bloomberg) -- Amgen Inc.’s osteoporosis drug
denosumab was approved by U.S. regulators for reducing fractures
in prostate and breast cancer patients, an indication that may
boost sales to $2.4 billion in five years.

The decision yesterday by the Food and Drug Administration
moves Amgen, based in Thousand Oaks, California, into the cancer
market with a drug cleared in June for treating osteoporosis in
older women. Denosumab will be marketed to reduce fractures and
surgery in patients whose breast, prostate or other solid tumors
have spread to their bones, Amgen said in a statement.

Amgen, the world’s largest biotechnology company, is
looking to denosumab to help revive growth, after revenue fell
2.4 percent last year. The drug will compete with Novartis AG’s
Zometa, which had 2009 sales of $1.47 billion. Denosumab, to be
sold as Xgeva, may reach sales of $2.4 billion in 2015, said
Yaron Werber, a Citigroup analyst in New York.

“This is a big, important step for the company, launching
a new product which will help put the company back on a growth
trajectory,” Werber said yesterday in a telephone interview.

Amgen fell 14 cents, to $55, at 4 p.m. New York time in
Nasdaq Stock Market composite trading. The shares have declined
1.9 percent in 12 months.

Sales of the drug may rise by an additional $500 million if
the company shows, in data expected this year, that denosumab
can keep cancer from spreading to bone, Werber said.

‘Enhance Appetite’

“If that works, that will make Xgeva a multibillion-dollar
product globally and dramatically enhance appetite for the
stock,” Werber said.

“This is the culmination of more than 15 years of effort
by our company,” said Roger Perlmutter, Amgen’s executive vice
president for research and development, in a telephone interview
yesterday. “This discovery provides the opportunity for
patients who have metastatic cancer affecting their bones to
have a therapy that improves their lives.”

Denosumab targets a protein called RANK ligand that Amgen
scientists discovered in the mid-1990s. This protein works with
others in a process that routinely breaks down old bone in the
body and replaces it with new. It also plays a role in weakening
the bones of people with osteoporosis and cancer.

Bone Destruction

When women’s estrogen levels fall after menopause, or when
cancer spreads to the bones from other parts of the body, the
change stimulates production of RANK ligand, intensifying bone
destruction. Denosumab, a synthetic version of an immune cell,
inhibits RANK ligand and reduces bone destruction, Perlmutter
said in a Nov. 15 telephone interview.

The most common serious side effects of denosumab seen in
clinical trials were low calcium levels in the blood and
osteonecrosis, or bone decay, in the jaw, Amgen said in the
statement. The bone loss occurred about as often with denosumab
as it did with Zometa, while low calcium was more common among
users of denosumab, Amgen said. In one study of prostate cancer
patients, 2.6 percent of those taking denosumab developed
osteonecrosis, the company said.

In breast and prostate cancer patients, malignant cells
spread to bone in about 65 percent to 75 percent of cases,
according to research published in the journal Cancer in 2000.
When the tumors replace healthy bone tissue, it may cause pain,
swelling and fractures and need to be treated with radiation,
chemotherapy or amputation.

Skeletal-Related Events

Amgen conducted a series of studies that measured how long
it took on average for patients taking either denosumab or
Zometa to experience their first “skeletal-related event,” a
fracture, spinal cord compression, or the need for surgery or
radiation.

One of these studies, submitted to the FDA, showed
denosumab delayed broken bones and complications 20.7 months, or
three months longer than Zometa in 1,901 prostate cancer
patients whose tumors had spread to their bones. In another
study of 2,046 breast cancer patients, denosumab delayed
fractures or complications longer than Zometa, Perlmutter said.

Denosumab also kept fractures at bay longer than Zometa in
patients with a variety of other tumor types, although the
difference wasn’t statistically significant, Perlmutter said.
For patients with multiple myeloma, Zometa outperformed
denosumab. While the drug wasn’t approved yesterday for myeloma,
Amgen is starting a new study of patients with that condition.

Osteoporosis Sales

Denosumab’s use in osteoporosis since it was approved has
lagged behind analyst’s predictions. It had $10 million in sales
in the quarter ended Sept. 30, below the $31 million expected by
analysts surveyed by Bloomberg.

Sales for treating osteoporosis are likely to increase as
doctors become comfortable with the medicine and get used to a
complicated billing system, said Robyn Karnauskas, an analyst
with Deutsche Bank Securities in New York, in a Nov. 15 note to
investors. Use in cancer presents the biggest opportunity, she
said.

That’s partly because tumor patients should get the drug 12
times a year, compared with twice-yearly shots for osteoporosis
patients, Perlmutter said. The recommended dose for people with
cancer is also twice as large.